Prepare noodles according to package directions, drain and set aside. In a large, nonstick saute pan, combine soy sauce, brown sugar and red pepper flakes. Stir to dissolve sugar. Add onions, garlic and gingerroot. Cook for 2 minutes. Add snow peas, scallions and lime peel. Toss and cook until peas are tender and bright colored, about 1 to 2 minutes. Add bean sprouts and tofu. Continue cooking and toss just until bean sprouts are slightly wilted. Add noodles and toss to mix. Add lime juice to taste and garnish with cilantro. Serve hot.